Strange Ancient Ape Walked on All Fours

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A bizarre ancient ape whose gait has stumped researchers for
decades walked on all fours and swung from the trees, new
research suggests.

Oreopithecus bambolii, an ape that lived on an isolated
island 7 million to 9 million years ago in what is now Tuscany
and Sardinia, Italy, didn't have the pelvis or spine necessary
for regular
upright walking, the researchers said. Rather, the beast
traversed Earth on all fours.

Their conclusion, detailed online July 23 in the Journal of Human
Evolution, overturns an earlier hypothesis that the mysterious
ape independently evolved bipedal, or two-legged, walking.

Ape oddity

When O. bambolii was alive, Italy formed a string of
islands that were covered with swampy forests and teeming with
crocodilians. The ape went extinct after a land bridge
connected their island to other land, allowing large
saber-toothed cats and other predators to stalk the island.

But the strange creature was a bit of a mystery: Scientists
couldn't decide whether it was an ape or a monkey. (Apes have
longer arms for swinging through trees, and monkeys often have
tails that let them grab branches). O. bambolii had
apelike arms, odd teeth with ridges more like a monkey's and feet
that each had one backward-pointing toe, similar to those found
on birds. [ Image
Gallery: Our Closest Human Ancestor ]

"It's always been a kind of controversial beast. It's an ape
that's not closely related to any living apes at all," said
William Jungers, a physical anthropologist at Stony Brook
University in New York who was not involved in the study.

In the 1990s, one group of researchers took a second look at
O. bambolii's pelvis and spine, and concluded the animal
had adapted to walk on two legs.

That was a bold claim.

Because no other mammals, aside from humans and their ancestors,
routinely walked upright, anthropologists use bipedal adaptations
to determine which fossil apes are in humans'
direct evolutionary lineage, said study co-author Liza
Shapiro, an anthropologist at the University of Texas at Austin.

If O. bambolii, which isn't considered a direct ancestor
to humans, had independently evolved upright walking, that line
of logic would have to be rethought.

"It would be really extraordinary to see an animal we don't think
is closely related to us who got around this way," said William
Sanders, a paleoanthropologist at the University of Michigan who
was not involved in the study.

Second look

Shapiro and her colleague Gabrielle Russo, an anatomist at
Northeast Ohio Medical University, decided to take a second look
at O. bambolii.

The team carefully analyzed a fossilized Oreopithecus
skeleton that was discovered by a French paleontologist in 1872.

Prior research suggested this specimen had a wider pelvis
compared with apes' and a unique lower-back curvature called
lordosis. Both of these features give humans better balance when
walking upright.

But Shapiro's team looked at the skeleton from several
perspectives and found no evidence of these changes: no
lower-back curvature and no widening of the pelvis. It also
lacked the distinctive widening of vertebrae at the base, which
allows the human spine to stack like a pyramid and efficiently
direct force into the pelvis.